PCI_ScanBusForNonBridge() has two loops, first searching for
non-bridges and second that looks for bridges. The second loop has
hints in a debug print it should do recursion for buses underneath the
bridge but no recursion is attempted.

Since the second loop is quite useless in its current form, just
eliminate it. This code hasn't been touched for very long time so
either it's unused or the missing parts are not important enough for
anyone to attempt to add them.

Leave only a simple comment about the missing recursion for the
unlikely case that somebody comes across the lack of functionality. In
any case, search whether an endpoint exists downstream of a bridge
sounds generic enough to belong to core so if the functionality is to
be extended it should probably be moved into PCI core.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
---
 drivers/pci/hotplug/cpqphp_pci.c | 30 +++++++++++-------------------
 1 file changed, 11 insertions(+), 19 deletions(-)

diff --git a/drivers/pci/hotplug/cpqphp_pci.c b/drivers/pci/hotplug/cpqphp_pci.c
index 558866c15e03..b2efc4a90864 100644
--- a/drivers/pci/hotplug/cpqphp_pci.c
+++ b/drivers/pci/hotplug/cpqphp_pci.c
@@ -190,8 +190,7 @@ static int PCI_ScanBusForNonBridge(struct controller *ctrl, u8 bus_num, u8 *dev_
 {
 	u16 tdevice;
 	u32 work;
-	int ret;
-	u8 tbus;
+	int ret = -1;
 
 	ctrl->pci_bus->number = bus_num;
 
@@ -208,26 +207,19 @@ static int PCI_ScanBusForNonBridge(struct controller *ctrl, u8 bus_num, u8 *dev_
 			*dev_num = tdevice;
 			dbg("found it !\n");
 			return 0;
-		}
-	}
-	for (tdevice = 0; tdevice < 0xFF; tdevice++) {
-		/* Scan for access first */
-		if (!pci_bus_read_dev_vendor_id(ctrl->pci_bus, tdevice, &work, 0))
-			continue;
-		ret = pci_bus_read_config_dword(ctrl->pci_bus, tdevice, PCI_CLASS_REVISION, &work);
-		if (ret)
-			continue;
-		dbg("Looking for bridge bus_num %d dev_num %d\n", bus_num, tdevice);
-		/* Yep we got one. bridge ? */
-		if ((work >> 8) == PCI_TO_PCI_BRIDGE_CLASS) {
-			pci_bus_read_config_byte(ctrl->pci_bus, PCI_DEVFN(tdevice, 0), PCI_SECONDARY_BUS, &tbus);
-			/* XXX: no recursion, wtf? */
-			dbg("Recurse on bus_num %d tdevice %d\n", tbus, tdevice);
-			return 0;
+		} else {
+			/*
+			 * XXX: Code whose debug printout indicated
+			 * recursion to buses underneath bridges might be
+			 * necessary was removed because it never did
+			 * any recursion.
+			 */
+			ret = 0;
 		}
 	}
 
-	return -1;
+
+	return ret;
 }
 
 
-- 
2.39.5

On Thu, Oct 17, 2024 at 05:31:31PM +0300, Ilpo Järvinen wrote:
> PCI_ScanBusForNonBridge() has two loops, first searching for
> non-bridges and second that looks for bridges. The second loop has
> hints in a debug print it should do recursion for buses underneath the
> bridge but no recursion is attempted.
> 
> Since the second loop is quite useless in its current form, just
> eliminate it. This code hasn't been touched for very long time so
> either it's unused or the missing parts are not important enough for
> anyone to attempt to add them.
> 
> Leave only a simple comment about the missing recursion for the
> unlikely case that somebody comes across the lack of functionality. In
> any case, search whether an endpoint exists downstream of a bridge
> sounds generic enough to belong to core so if the functionality is to
> be extended it should probably be moved into PCI core.
> 
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
> ---
>  drivers/pci/hotplug/cpqphp_pci.c | 30 +++++++++++-------------------
>  1 file changed, 11 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/pci/hotplug/cpqphp_pci.c b/drivers/pci/hotplug/cpqphp_pci.c
> index 558866c15e03..b2efc4a90864 100644
> --- a/drivers/pci/hotplug/cpqphp_pci.c
> +++ b/drivers/pci/hotplug/cpqphp_pci.c
> @@ -190,8 +190,7 @@ static int PCI_ScanBusForNonBridge(struct controller *ctrl, u8 bus_num, u8 *dev_
>  {
>  	u16 tdevice;
>  	u32 work;
> -	int ret;
> -	u8 tbus;
> +	int ret = -1;
>  
>  	ctrl->pci_bus->number = bus_num;
>  
> @@ -208,26 +207,19 @@ static int PCI_ScanBusForNonBridge(struct controller *ctrl, u8 bus_num, u8 *dev_
>  			*dev_num = tdevice;
>  			dbg("found it !\n");
>  			return 0;
> -		}
> -	}
> -	for (tdevice = 0; tdevice < 0xFF; tdevice++) {
> -		/* Scan for access first */
> -		if (!pci_bus_read_dev_vendor_id(ctrl->pci_bus, tdevice, &work, 0))
> -			continue;
> -		ret = pci_bus_read_config_dword(ctrl->pci_bus, tdevice, PCI_CLASS_REVISION, &work);
> -		if (ret)
> -			continue;
> -		dbg("Looking for bridge bus_num %d dev_num %d\n", bus_num, tdevice);
> -		/* Yep we got one. bridge ? */
> -		if ((work >> 8) == PCI_TO_PCI_BRIDGE_CLASS) {
> -			pci_bus_read_config_byte(ctrl->pci_bus, PCI_DEVFN(tdevice, 0), PCI_SECONDARY_BUS, &tbus);
> -			/* XXX: no recursion, wtf? */
> -			dbg("Recurse on bus_num %d tdevice %d\n", tbus, tdevice);
> -			return 0;
> +		} else {
> +			/*
> +			 * XXX: Code whose debug printout indicated
> +			 * recursion to buses underneath bridges might be
> +			 * necessary was removed because it never did
> +			 * any recursion.
> +			 */
> +			ret = 0;

I'm OK with this except that I wonder if we should leave an actual
info or even warning level printk here as a more visible debugging
hint if somebody hits this.  I'm not sure that simply returning 0
would be enough of a hint about why devices below the bridge weren't
found.

>  		}
>  	}
>  
> -	return -1;
> +
> +	return ret;
>  }
>  
>  
> -- 
> 2.39.5
>